The present invention is directed to a continuous and exceptionally efficient method and apparatus of producing gaseous chlorine dioxide by the reaction between gaseous sulfur dioxide and an aqueous solution of a metallic chlorate.
In the past, a number of commercial methods have been developed for producing chlorine dioxide for use primarily as a bleaching agent and disinfectant. One such method involves the interaction of a metallic chlorate (usually sodium chlorate) and a strong acid, with or without an accompanying chloride, as described in the following U.S. Pat. Nos. 2,664,341; 2,863,722; 3,563,702; 3,789,108; 3,974,266. However the relative chemical inefficiency, resultant high cost of chemicals, hazards from "puffing" (explosions caused by spontaneous decomposition of the chlorine dioxide) and the accompanying generation of usually unwanted chlorine all detract from the desirability of this method. In this connection, U.S. Pat. No. 2,481,241 addresses the need for separating the unwanted chlorine produced by this method from the chlorine dioxide.
Another commercial method which has been practiced in the past produces chlorine dioxide by reacting sodium chlorite either with chlorine gas or a combination of sodium hypochlorite and a strong acid, as shown in the following U.S. Pat. Nos. 4,234,446; 4,247,531; 4,250,144. Unfortunately sodium chlorite is approximately four to five times as costly as sodium chlorate, which renders the method too costly.
A third method utilizes an intermediate reductant such as methanol or sulfur dioxide in combination with a metallic chlorate, usually sodium chlorate, as shown in the following U.S. patents the disclosures of which are hereby incorporated by reference: U.S. Pat. Nos. 2,481,240; 2,598,087; 3,950,500; 4,250,159. Such method is desirable because it utilizes the relatively inexpensive chlorate reactant, and normally does not produce unwanted chlorine gas. However the chemical inefficiency of the method in the past, and its hazards from possible "puffing", have remained as serious drawbacks. Moreover, it has not been known how to improve the efficiency of the method without also increasing the safety hazards incident to "puffing" and high heat generation which would accompany any such increase in efficiency. Nor is it known how to improve the efficiency of the reaction compatibly with generation of the chlorine dioxide in a form free from the spent reactants, so that the chlorine dioxide may be used for producing potable water or treating foodstuffs.